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ANOTHER  CONIDIAL  SCLEROSPORA  OF  PHILIPPINE 

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WILLIAM  H.  WESTON,  Jr. 


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Reprinted  from  JOURNAL  OF  AGRICULTURAL  RESEARCH 
Vol.  XX,  No.  9  :  :  :  :  Washington,  D.  C-,  February  1,  1921 


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PUBLISHED  BY  AUTHORITY  OF  THE  SECRETARY  OF  AGRICULTURE,  WITH 
THB  COOPERATION  OF  THE  ASSOCIATION  OF  LAND-GRANT  COLLEGES 


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WASHINGTON  :  GOVERNMENT  PRINTING  OFFICE  :  1921 


— 1 


ANOTHER  CONIDIAE  SCLEROSPORA  OF  PHIEIPPINE 


Each  year  in  the  Philippine  Islands  the  valuable  maize  crop  suffers 
very  severe  losses  from  the  destructive  activities  of  downy  mildew  ( Scleros - 
pora  spp.) .  While  the  writer  was  studying  this  disease  during  the  past 
two  years  his  attention  was  naturally  directed  to  the  question  whether 
the  widespread  destruction  of  maize  throughout  the  thousand-mile  extent 
of  these  scattered  islands  was  due  in  all  cases  to  the  same  species  of 
fungus.  A  comparative  study  of  material  collected  from  many  parts  of 
the  provinces  of  Batangas,  Laguna,  and  Rizal  in  the  island  of  Luzon, 
where  the  disease  is  most  serious  and  where  it  was  studied  most  inti¬ 
mately,  showed  that  in  all  cases  the  same  causal  fungus  was  involved. 
This  species  of  downy  mildew  was  described  in  an  earlier  paper  (12)1  as 
Scleros  pora  philip  pinensis.  It  was  only  natural  to  suspect  that  some  of 
the  abundant  Philippine  wild  grasses  related  more  or  less  closely  to  maize 
would  be  found  to  harbor  this  or  other  Sclerosporas.  As  on  the  widely 
distributed  wild  grass  Saccharum  spontaneum  L.  (PL  77,  A)  the  oogonial 
stage  of  a  Sclerospora  had  been  very  commonly  encountered  in  great 
abundance,  this  grass  was  obviously  an  object  of  suspicion.  In  Luzon, 
however,  despite  extensive  search,  no  conidial  stage  was  seen  on  this  host. 

During  a  trip  to  the  more  southern  Visayan  Islands  of  Cebu,  Bohol, 
and  Leyte,  in  which  maize  is  a  crop  of  very  great  importance,  the  writer 
found  that  there,  also,  the  maize  plantings  were  suffering  heavy  losses 
from  downy  mildew.  As  no  microscope  was  carried,  no  study  of  the 
causal  organism  was  made  at  night  during  the  period  of  conidium  pro¬ 
duction.  However,  inasmuch  as  the  symptoms  and  the  general  effect  of 
the  downy  mildew  were  the  same  in  these  southern  islands,  the  writer 
inferred  that  the  causal  organism  was  that  which  he  had  found  so  widely 
distributed  on  maize  throughout  the  northern  island  of  Luzon.  Also  the 
wild  grasses  of  these  southern  islands  were  carefully  examined  as  possible 


1  Reference  is  made  by  number  (italic)  to  “  Literature  cited,”  p.  684. 


Journal  of  Agricultural  Research, 
Washington,  D.  C. 
wq 


Vol.  XX,  No.  9 
Feb.  1,  1921 
Key  No.  G-217 


(669) 


« 


Journal  of  Agricultural  Research 


Vol.  XX,  No.  9 


kh  f  l  |  ,i 

670 


hosts  for  downy  mildew.  After  long  search  a  clump  of  bugang  grass 
( Saccharum  spontaneum )  heavily  infected  by  a  conidial  Sclerospora  was 
discovered  by  Mrs.  Weston.  Continued  hunting  brought  the  fungus  to 
light  on  the  same  host  in  two  other  places,  all  three  cases  being  encoun¬ 
tered  in  the  rugged  interior  uplands  of  Cebu  (PL  76),  which  lie  between 
Carcar  and  Barili.  In  the  island  of  Leyte,  also,  this  Sclerospora  was 
again  found  on  bugang  grass  on  a  hillside  about  three  miles  from  Bavbay. 
No  other  cases  of  downy  mildew  either  on  this  or  on  other  hosts  were  seen. 
Later,  in  a  field  of  native  sugar  cane  near  Guadelupe  cemetery  outside 
the  town  of  Cebu,  a  single  clump  of  cane  was  found  infected  with  the 
conidial  stage  of  a  Sclerospora. 

The  infected  plants  of  Saccharum  spontaneum  and  sugar  cane  were 
transplanted  to  Los  Banos,  Luzon,  for  further  study  (PI.  77,  B).  There 
a  comparison  of  living  material  taken  from  these  plants  during  the  opti¬ 
mum  time  of  nocturnal  conidiophore  production  showed  that  this  downy 
mildew  from  the  southern  islands  was  different  from  that  previously 
studied  in  Luzon.  This  discovery  necessitated  a  revision  of  all  available 
material  in  order  to  determine  whether  or  not  other  forms  had  been  pre¬ 
viously  overlooked  under  the  assumption  that  the  collections  were  all 
of  the  same  form  so  commonly  found  in  Luzon.  Accordingly,  living 
material  from  maize,  teosinte,  and  sorghum  from  the  college  plots  and 
from  native  fields  in  Batangas  and  Laguna  provinces  was  compared  with 
the  living  material  from  the  plants  of  Saccharum  spontaneum  and  sugar 
cane  brought  from  Cebu.  Dried,  preserved,  and  mounted  specimens 
from  maize  collected  in  various  parts  of  Luzon  were  compared  with  similar 
specimens  from  maize  obtained  in  various  localities  in  Cebu,  Bohol,  and 
Leyte.  This  survey  showed  clearly  that  all  the  material  so  far  encoun¬ 
tered  fell  into  one  or  the  other  of  two  distinct  species — one,  the  form 
with  shorter,  broader  conidia  found  on  maize,  etc.,  in  Luzon  and  pre¬ 
viously  described  as  Sclerospora  philip pinensis,  and  the  other,  which  will 
be  called  Sclerospora  spontanea,  characterized  by  longer,  narrower  conidia, 
and  found  on  maize,  bugang  grass,  and  sugar  cane  in  the  Visayas.  Once 
this  point  had  been  established,  a  comprehensive  study  was  made  of  the 
two  species  to  determine  the  resemblances  and  differences  between  them 
in  morphological  and  physiological  characteristics. 


COMPARATIVE  STUDY  OF  SCLEROSPORA  PHILIPPINENSIS  AND 

SCLEROSPORA  SPONTANEA 


FIELD  CHARACTERISTICS 

On  maize,  as  observed  in  the  field  in  the  more  southern  islands  and  in 
Luzon,  the  two  species  are  apparently  identical  in  their  destructiveness 
to  the  crop  as  a  whole  and  also  in  their  effect  on  the  individual  plants. 
It  is  possible  that  quantitative  studies  of  essentially  similar  fields  infected 
by  the  separate  species  would  show  some  slight  differences,  but  in  general 
appearance  there  is  no  distinction  whatever  between  the  two. 


Feb. i, i92i  Another  Conidial  Sclerospora  of  Philippine  Maize  671 


PHYSIOLOGICAL  CHARACTERISTICS 

1 

Several  varieties  of  maize  grown  in  sterile  soil  and  under  controlled 
conditions  preventing  contamination  were  infected  with  spores  produced 
on  the  living  plants  of  bugang  grass  ( Saccharum  spontaneum )  and  sugar 
cane  brought  from  Cebu.  Parallel  inoculations  were  made  also  with 
Sclerospora  philip pinensis.  No  difference  was  apparent  either  in  symp¬ 
toms  or  in  the  virulence  of  the  resulting  infection.  Similar  experiments 
with  seedlings  of  cultivated  wheat,  Setaria,  Pennisetum,  and  several 
species  of  wild  grasses,  including  the  very  common  aguingay  ( Rottboellia 
exaltata  L.),  anias  ( Andropogon  sorghum  var.  halepense  L.),  cogon  ( Impe - 
rata  cylindracea  L.),  and  tigbee  ( Coix  lachryma-jobi  L.),  using  the  long, 
narrow  conidia  of  the  southern  species,  were  as  uniformly  unsuccessful 
as  they  had  been  with  Sclerospora  philip  pinensis  ( 12 ).  Seedlings  of 
teosinte  (Euchlaena  luxurious  Schrad.)  and  the  wild  grasses,  Saccharum 
spontaneum  and  Miscanthus  japonicus  (Thunb.)  Anders.,  were  success¬ 
fully  inoculated  with  both  forms.  No  seeds  of  sugar  cane  were  available 
for  planting.  Had  there  been,  there  is  little  doubt  in  the  mind  of  the 
writer  that  infections  in  this  case  also  could  have  been  obtained.  A 
more  detailed  account  of  these  inoculation  experiments  will  be  given  in 
a  later  paper.  It  should  be  said  here,  however,  that  the  effect  of  the 
Sclerosporas  varied  with  the  different  hosts,  being  most  destructive  on 
maize  and  least  so  on  bugang  grass ;  but  the  characteristic  production  of 
conidiophores  took  place  with  uniform  regularity  at  night  on  all 
(PI.  78,  B). 

A  comparative  study  of  material  of  Sclerospora  spontanea  on  these 
different  hosts  showed  that  the  distinguishing  morphological  character¬ 
istics  of  the  fungus  had  not  been  altered  in  any  way.  Moreover,  even 
after  transition  from  one  host  to  another  through  several  generations, 
the  species  remained  constant  and  in  no  way  approached  S.  philip  pinensis. 
In  like  manner,  after  inoculating  various  hosts  and  passing  through 
several  generations,  S.  philip  pinensis  also  was  quite  unchanged  and 
showed  no  tendency  to  approach  the  long-spored  form. 

The  writer  considers  it  quite  possible  that  an  exact  statistical  study  of 
large  numbers  of  individuals  infected  by  each  of  the  two  fungi  would 
reveal  some  slight  quantitative  difference  in  the  area  bearing  conidia,  or 
in  the  rate  of  growth  of  hyphae  through  the  host,  or  in  some  other  aspect 
not  at  once  apparent  to  an  ordinary  comparative  examination.  It 
should  be  noted  here,  however,  that  there  is  certainly  no  noticeable 
physiologic  difference  between  the  two  in  virulence,  range  of  hosts,  or 
general  course  of  the  resulting  disease  they  produce. 

MORPHOLOGICAL  CHARACTERISTICS 

Therefore,  because  the  two  forms  differ  morphologically  rather  than 
physiologically,  they  were  carefully  compared  in  order  to  determine 
whether  the  points  of  difference  were  sufficiently  stable  and  well  marked 


672 


Journal  of  Agricultural  Research 


Vol.  XX,  No.  9 


to  establish  the  long-spored  form  as  a  species  distinct  from  Sclerospora 
philip  pinensis. 

Mycelium. — In  morphological  characteristics,  extent,  and  relation  to 
the  host  tissue,  the  mycelium  of  the  two  fungi  showed  no  distinctions 
sufficiently  marked  or  unvarying  to  warrant  their  use  as  a  basis  of 
separation.  However,  the  club-shaped  hyphae  (conidiophore  initials) 
which  grow  out  through  the  stomata  and  develop  into  conidiophores  are 
different  in  the  two  forms,  those  of  the  long-spored  Sclerospora  being 
markedly  longer,  more  slender,  and  more  irregular. 

Conidiophores. — In  general  appearance  the  conidiophores  of  the  two 
Sclerosporas  are  noticeably  dissimilar,  those  of  the  Visayan  form  being 
markedly  longer,  more  slender,  and  more  spreadingly  branched  than 
those  of  Sclerospora  philip  pinensis.  On  analyzing  this  dissimilarity  the 
details  of  difference  discussed  in  the  following  paragraphs  are  apparent. 

The  basal  cell  of  the  Visayan  Sclerospora  is  very  long  (PI.  79,  A,  D, 
E,  F,  H),  strikingly  longer  than  that  of  Sclerospora  philip  pinensis.  The 
length  (140  to  260  R)  is  greater  not  only  actually  but  also  relatively,  for 
even  in  the  unusual  cases  when  it  is  less  conspicuously  long  (PI.  79,  G) 
the  basal  cell  of  the  Visayan  Sclerospora  always  exceeds  or  at  least  equals 
in  length  that  part  of  the  main  axis  extending  from  the  terminal  septum 
of  the  basal  cell  to  the  origin  of  the  primary  branches.  In  S.  philippi- 
nensis,  the  basal  cell  is  always  shorter  than  this  part  of  the  main  axis. 
Moreover,  the  basal  cell  of  the  Visayan  Sclerospora  is  much  more  slender, 
usually  5  to  8  /x  at  its  narrowest  diameter,  and  much  less  knobbed  or 
swollen  at  its  base  (PI  79,  A,  D,  E,  F,  H)  than  is  the  basal  cell  of  5. 
philip  pinensis. 

The  main  axis  of  the  Visayan  Sclerospora  expands  more  abruptly 
above  the  basal  cell  and  then  constricts  more  distinctly  (PI.  79,  A,  D) 
just  below  the  branches  than  in  Sclerospora  philip  pinensis.  The  greatest 
diameter  (22  to  32  fi),  which  usually  slightly  exceeds  that  of  5.  philip- 
pinensis,  is  thus  placed,  not  just  below  the  branches  (as  in  S.  philip - 
pinensis ),  but  some  distance  lower  (PI.  79,  A,  D,  G,  H). 

The  branches  of  the  Visayan  form  generally  are  less  constricted  at 
their  point  of  origin,  are  of  more  uniform  diameter,  and  are  straighter, 
less  ascending,  more  spreading,  and  do  not  recurve,  but  stand  out  from 
the  main  axis  more  stiffly.  They  are  characteristically  longer  and  more 
slender,  but,  even  if  short  and  crowded,  they  stand  out  more  stiffly  than 
in  Sclerospora  philip  pinensis.  Although  varying  considerably  in  both 
species,  the  number  of  conidia  produced  on  conidiophores  is  approxi¬ 
mately  the  same  in  S.  spontanea  and  in  5.  philip  pinensis.  In  the  former, 
32  to  48  are  commonly  borne,  although  as  many  as  88  or  as  few  as  12 
may  less  frequently  occur. 

The  sterigmata  also  are  straighter,  less  recurved,  and  stand  out  more 
stiffly  than  in  Sclerospora  philip  pinensis,  and,  usually  they  are  longer 
(about  1 3  ju).  It  should  be  noted,  however,  that  the  length  varies  with 


Feb.  i,  1921 


Another  Conidial  Sclerospora  of  Philippine  Maize  673 


the  extent  of  the  branch  system,  since  in  cases  where  this  is  reduced  and 
the  primary  branches  or  even  the  main  axis  give  rise  directly  to  sterig- 
mata,  these  sterigmata  are  much  larger  (PI  79,  B)  than  they  are  when 
arising  from  quaternary  or  tertiary  branches  as  the  ultimate  structures 
of  an  elaborate  system  (PI.  79,  A). 

As  a  result  of  such  differences,  the  conidiophore  top  of  the  Visayan 
Sclerospora  has  a  more  spreading,  expanded  appearance;  and  the  long 
axes  of  the  branches,  the  sterigmata,  and  the  conidia  borne  on  them 
stand  out  from  the  main  axis  like  rays  of  a  partly  opened  fan.  In 
Sclerospora  philip pinensis ,  on  the  contrary,  the  conidiophore  top  is  more 
compact  and  less  spreading,  the  axes  of  branches,  sterigmata,  and 
conidia  being  all  approximately  parallel  to  each  other  and  to  the  main 
axis. 

% 

These  differences  in  the  conidiophores  of  the  two  fungi  are,  on  the 
whole,  relative  rather  than  absolute  and  are  influenced  to  some  extent 
by  such  environmental  conditions  as  the  depth  and  persistence  of  the 
layer  of  dew  in  which  they  develop.  Even  these  distinctions,  however, 
could  be  used  as  more  absolute  and  less  relative  criteria  if  a  very  large 
number  of  measurements  of  all  parts  of  the  conidiophores  were  made 
and  assembled  to  give  an  adequate  quantitative  impression.  Even 
from  the  qualitative  rather  than  quantitative  point  of  view,  moreover, 
these  differences,  although  relative,  are  constant  and  distinct,  and  it 
should  be  emphasized  that  they  persist  when  the  two  fungi,  developing 
under  exactly  parallel  circumstances  on  sister  plants  of  the  same  age, 
grown  side  by  side  under  as  nearly  the  same  conditions  of  temperature, 
soil,  dew  deposition,  etc.,  as  it  was  possible  to  obtain,  were  compared 
by  nightly  examinations  for  several  weeks. 

Conidia. — Among  the  Peronosporaceae  as  a  whole  the  characteristics 
of  the  conidia  have  been  found  to  be  the  most  valuable  basis  for  dis¬ 
tinguishing  species.  This  applies  equally  well  to  these  two  Sclerosporas, 
since  their  conidia  not  only  differ  markedly  and  constantly  in  shape  and 
size  but  also  remain  relatively  unaffected  by  changes  in  environment 
and  hosts. 

In  shape,  the  conidia  of  the  Visayan  Sclerospora  are  at  once  distin¬ 
guished  from  those  of  Sclerospora  philip pinensis .  They  are  not  only 
much  more  elongate  but  much  more  slender  as  well,  the  length  being 
frequently  two  or  even  three  times  the  diameter.  Consequently  they 
range  from  very  elongate  ovoid  and  obovoidal  bodies  to  long  narrow, 
round-ended  cylinders,  but  they  are  most  commonly  very  elongately 
ellipsoid  in  shape.  A  clearer  idea  of  these  variations  may  be  gained 
from  Plate  79,  I,  J,  K. 

In  such  features  as  the  rounded  apex  devoid  of  any  papilla,  the  blunt 
base  with  its  apiculus  of  attachment,  the  hyaline,  granular  content, 
and  the  thin  wall,  the  conidia  correspond  to  those  of  Sclerospora 


674 


Journal  of  Agricultural  Research 


Vol.  XX,  No.  9 


philip pinensis .  As  in  the  case  of  the  latter  species  also,  germination 
is  invariably  by  the  protrusion  of  one  or  more  germ  tubes  (PI.  79,  I, 

L  K)-  . 

In  size,  the  conidia  of  the  Visayan  Sclerospora  are  very  variable. 
With  respect  to  such  widely  varying  bodies  as  the  spores  of  this  and 
other  genera  of  Peronosporaceae,  recent  investigations  have  shown  that 
it  is  no  longer  possible  to  delimit  a  species  adequately  by  the  extremes 
or  averages  of  a  few  measurements.  Rather,  there  is  required  the 
assembling  and  presentation  in  tables  and  graphs  of  a  sufficiently  large 
number  of  representative  measurements  to  give  a  quantitative  as  well 
as  a  qualitative  expression  of  the  conidial  characteristics  of  the  species. 

Accordingly,  in  order  to  obtain  data  adequate  to  identify  the  Visayan 
form  and  to  furnish  a  basis  for  comparing  it  with  others,  700  conidial 
measurements  were  made.  These  comprised  measurement  groups  of 
100  conidia  from  each  of  the  two  sugar-cane  and  the  four  Saccharum 
spontaneum  plants  from  Cebu,  and  from  one  maize  plant  inoculated 
from  the  latter. 

The  conidia  were  taken  from  the  leaves  of  the  host  at  night  during 
the  optimum  period  of  conidia  production — from  2  to  4  a.  m. — mounted 
in  dew,  and  measured  immediately. 

Since,  on  examination,  the  seven  measurement  groups  were  found  to 
agree  in  all  essential  particulars,  they  were  combined  into  the  total  of 
700.  For  the  purposes  of  comparison,  700  measurements  of  Sclerospora 
philip  pinensis  were  secured  in  like  manner.1  Of  these,  300  were  new 
ones  made  of  fresh  conidia  from  teosinte  and  sorghum  found  infected  in 
the  college  plots  and  from  Saccharum  spontaneum  seedlings  artificially 
inoculated  from  maize.  All  these  groups  were  compared,  found  to  agree, 
and  grouped  into  the  total  of  700. 

In  making  these  measurements,  care  was  taken  to  include  every 
conidium  in  a  marked  area  of  the  microscope  field  as  the  slide  was  moved 
along  by  the  mechanical  stage.  Only  those  conidia  obviously  injured  or 
those  still  attached  to  the  conidiophores  were  excluded.  The  divisions 
of  the  eyepiece  equaled  approximately  1.8  /x,  and,  with  the  magnification 
used,  it  was  possible  to  estimate  with  fair  accuracy  to  one-third  of  a 
division,  or  to  about  0.6  /z.  Consequently,  the  measurements  are  exact 
to  this  extent — that  is,  the  conidium  recorded  as  32  n  in  length  may  as 
well  be  31.4  /x  or  32.6  /x  instead  of  exactly  32  /z  but  not,  in  all  probability, 
3 1  or  33  ix.  With  a  large  number  of  spores  such  differences  tend  to  equalize 
themselves.  As  a  result,  the  measurements  presented  here  may  be 
considered  as  adequately  representing  the  characteristics  of  the  conidia 
of  the  species  involved. 

1  The  writer  wishes  to  take  this  opportunity  to  call  attention  to  an  error  in  the  tabulation  of  the  previous 
spore  measures  of  Sclerospora  philip  pinensis  (/2,  p.  no).  In  the  table  of  length,  the  conidia  measuring  41 
to  42.9  m  should  be  2 3  in  number  instead  of  24. 


Feb.  i,  1921 


Another  Conidial  Sclerospora  0)  Philippine  Maize  675 


The  measurements  are  summed  up  in  Table  I  and  are  presented  in 
graphic  form  in  figure  1.  In  addition,  the  biometric  characteristics  of 
the  two  species  are  given  in  Table  II.  In  making  the  calculations,  the 
directions  and  formulae  of  E.  Davenport  (3)  and  C.  B.  Davenport  (2) 


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nPT/O  Or  LE/VGTH  TO  O/AMSTSf? 


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Q/FMF  TOP  OF  COM 0*9  l/J 
N/CPONS 


Fig.  i . — Comparison  of  the  sizes  of  700  conidia  of  Sclerospora  spontanea  with  700  eonidia  of  S.  philip pinensis; 
A,  variation  of  conidia  in  length;  B,  variation  of  conidia  in  diameter;  C,  ratios  of  length  to  width  of 
conidia  arranged  in  classes. 


have  been  followed.  The  writer  makes  no  pretense  to  a  comprehensive 
biometric  study  of  the  two  Sclerosporas  but  has  used  this  method  solely 
as  a  means  to  the  end  of  presenting  the  accompanying  data  as  a  basis 
of  comparison  between  these  and  other  species. 


676 


Journal  of  Agricultural  Research 


Vol.  XX,  No.  9 


Table  I. — Summarized  measurements  of  conidia  of  Sclerospora  spontanea  and 

Sclerospora  philip  pinensis 


Length. 

Diameter. 

Length  over  diameter. 

N umber  of  conidia 

Number  of  conidia 

Number  of  conidia 

in  700. 

in 

*00. 

in  700. 

Ratio  classes. 

classes. 

Classes. 

5.  spon- 

S.  philip- 

S. spon- 

S.  philip- 

S. spon- 

■S.  philip  - 

tanea. 

pinensis. 

tanea. 

pinensis. 

tanea. 

pinensis. 

M- 

M- 

17  to  18.9. .  . 

I 

II  to  12.9. .  . 

II 

2 

0.95  to  1. 14 .  .  . 

19  to  20.9. .  . 

I 

13  to  14.9. .  . 

175 

18 

1. 15  to  1.34.  .  . 

21  tO  22.9.  .  . 

2 

15  to  16.9. .  . 

391 

119 

1.35  to  1.54.  .  . 

5 

23  to  24.9. .  . 

5 

17  to  18.9. .  . 

12 1 

311 

1.55  to  1.74. . . 

25  to  26.9. .  . 

.  1 

17 

19  to  20.9.  .  . 

2 

199 

1.75  to  1.94. . . 

7 

A>4 

2 1 1 

27  to  28.9. .  . 

3 

27 

21  tO  22.9.  .  . 

50 

1.95  to  2.14. . . 

28 

163 

29  to  30.9.  .  . 

10 

77 

23  to  24.9. .  . 

I 

2.15  to  2.34. . . 

92 

88 

31  to  32.9. .  . 

12 

134 

2.35  to  2.54. . . 

102 

24 

33  to  34.9. . . 

20 

153 

2.55  to  2.74. . . 

154 

8 

35  to  36.9.  •  • 

93 

107 

2.75  to  2.94-  •  • 

161 

4 

37  to  38.9. . . 

76 

75 

2.95  to  3.14. .  . 

88 

39  to  40.9. . . 

87 

39 

3.15  to  3.34.  .  . 

37 

41  to  42.9. . . 

112 

29 

3-35  to  3.54.  . . 

22 

43  to  44.9.  .  . 

94 

33 

3-55  to  3.74. .  . 

5 

45  to  46.9... 

79 

7 

3-75  to  3.94-  •  • 

3 

47  to  48.9.  . . 

46 

2 

3.95  to  4.14.  . . 

O 

49  to  50.9.  .  . 

22 

0 

4.15  to  4.34.  . . 

1 

51  to  52.9. .  . 

15 

1 

53  to  54.9... 

12 

55  to  56.9. . . 

7 

57  to  58.9. . . 

5 

59  to  60.9. .  . 

4 

61  to  62.9.  .  . 

0 

63  to  64.9. .  . 

2 

Table  II. — Biometric  constants  of  the  conidia  of  Sclerospora  spontanea  and 

Sclerospora  philip  pinensis 

LENGTH 


Species. 

Mean. 

Median. 

Mode 

(approx¬ 

imate). 

Standard  de¬ 
viation. 

Coefficient  of 
variability. 

S.  spontanea . 

•S',  philip  pinensis. . 

A*. 

42. 07±o.  145 
34-  S2  ±  .113 

»■ 

41. 86±o.  142 
34.  I2±  .142 

41-43 

33-32 

5.  672±o.  102 

4- 439  ±  -080 

i3-48±o.  247 
i2.86±  .235 

DIAMETER 

S.  spontanea . 

5.  Philip  pinensis. . 

»■ 

15-  79 ±0.  036 
18.  40±  .047 

M- 

15. 84  ±0. 045 

18. 36±  .006 

M- 

15-93 

18.36 

i.  395 ±0. 025 
i-834±  .033 

8.  83±o.  160 
9-97±  •  181 

RATIO  OF  LENGTH  TO  DIAMETER 

S.  spontanea . 

•S.  philip  pinensis. . 

2.  7i±o.  009 
i.  91  ±  .007 

2.  7i±o.  on 
i.89±  .00S 

2.  71 
1.85 

0.  357±o.  006 
.  266±  .005 

13.  20±o.  242 

13. 92±  .256 

An  examination  of  the  data  shows  clearly  that  the  long-spored  Visa van 
form,  Sclerospora  spontanea ,  at  least  in  regard  to  its  conidia,  is  quite  dis¬ 
tinct  from  5.  philip  pinensis.  The  location  of  the  two  frequency  curves 
shows  that  the  great  bulk  of  the  conidia  of  5.  philip  pinensis  fall  between 
the  limits  of  31  to  36.9  /i  in  length,  and  17  to  18.9  ju  in  width;  while,  on 
the  contrary,  a  like  proportion  of  those  of  S.  spontanea  are  37  to  46.9  /u 
in  length  and  15  to  16.9  m  in  width.  The  somewhat  irregular  character 


Feb.  i,  1921 


Another  Conidial  Sclerospora  of  Philippine  Maize  677 


of  the  length  curve  of  the  latter  species  does  not,  in  the  opinion  of  the 
writer,  indicate  that  it  is  bimodal,  because,  by  using  more  inclusive 
measurement  classes  of  4  /x  or  even  3  /*,  the  depression  so  noticeable  with 
the  2-/jl  classes  smooths  out  and  the  curve  becomes  quite  regular.  More¬ 
over,  the  difference  between  the  modes  as  well  as  between  the  means  and 
the  medians  is  still  sufficiently  great  to  emphasize  strikingly  the  dissimi¬ 
larity  in  size  of  the  conidia  of  the  two  species. 

It  should  be  noted  that,  although  the  curves  of  frequency  distribution 
of  the  two  species  overlap  slightly,  size  is  none  the  less  a  valuable  diag¬ 
nostic  criterion.  In  length,  for  instance,  the  curves  overlap  from  26  n, 
the  lowest  limit  of  the  Visayan  Sclerospora,  to  52  n,  the  highest  limit 
reached  by  Sclerospora  philip pinensis .  As  a  result,  it  might  be  con¬ 
tended  that  size  is  of  no  value  in  distinguishing  between  the  two  species 
when  applied  at  least  to  the  conidia  falling  between  these  limits.  While 
this  is  true  of  any  one  conidium,  experience  shows  that,  if  several  are 

measured,  exceedingly  few  are  to  be  found  in  this  disputed  region.  For 

* 

practical  purposes  even  50  unselected  conidia  of  each  species  are  suffi¬ 
cient  to  show  the  difference  between  them  without  any  confusion  due  to 
overlapping. 

It  is  also  worthy  of  note  that  the  curves  of  the  frequency  distribution 
of  700  conidia  in  both  the  Visayan  species  and  Sclerospora  philip  pinensis 
differ  in  no  essential  particular  from  those  of  500,  400,  or  even  as  few  as 
200  conidia. 

Furthermore,  in  the  ratios  of  length  to  width  of  their  conidia,  the  two 
species  also  show  marked  differences.  The  shorter,  broader  spores  of 
Sclerospora  philip  pinensis  most  commonly  show  ratios  of  1.55  to  2.14, 
while  in  5.  spontanea  the  greater  length  as  well  as  the  lesser  width  of  the 
conidia  is  expressed  by  the  predominant  ratios  of  2.35  to  2.94. 

In  order  to  determine  whether  the  differences  between  the  biometric 
characteristics  of  the  two  forms  were  indeed  significant,  the  method 
quoted  by  Rosenbaum  ( 11 )  from  Reitz  and  Smith  was  employed.  This 
method,  which  compares  the  difference  between  the  mean  or  other  con¬ 
stants  with  the  probable  error  of  the  difference,  shows  that  in  Sclerospora 
philip  pinensis  and  5.  spontanea  these  differences  without  doubt  are 
significant  and  can  not  be  the  result  of  mere  random  sampling.  This 
significance  is  clearly  brought  out  in  Table  III. 

Table  III. — Difference  in  means  of  Sclerospora  spontanea  and  Sclerospora  philip- 

pinensis  compared  to  the  probable  errors 


Difference  in  means. 

Difference  in  means  divided  by 
probable  error  of  difference. 

Length. 

Diameter. 

Length  over 
diameter. 

Length. 

Diameter. 

Length 

over 

diameter. 

7.55±o.  183 

M ' 

3. 61  ±0. 058 

* 

0.  798±o.  on 

41.27 

44. 96 

70-  39 

678 


Journal  of  Agricultural  Research 


Vol.  XX,  No.  9 


The  identity  of  the  long-spored,  Visayan  Sclerospora,  then,  is  clearly 
established  as  quite  distinct  from  Sclerospora  philip pinen sis.  Whether 
this  distinction  is  sufficient  to  entitle  the  former  to  specific  rank  depends 
somewhat  upon  the  judgment  of  the  investigator.  The  matter  could 
be  settled  with  greater  finality  if  the  two  fungi  were  to  be  grown  in  pure 
culture  and  compared  in  morphological  and  physiological  details  under 
the  controlled  conditions  of  the  laboratory,  but  unfortunately  all  attempts 
to  grow  the  two  forms  artificially  have  been  unsuccessful.  In  view, 
however,  of  such  well-defined,  although  somewhat  relative,  morphological 
differences  in  the  conidiophores  as  the  peculiarities  of  the  basal  cell  and 
the  branch  system,  and  the  well-marked  and  easily  measurable  differ¬ 
ences  in  size  and  shape  between  the  conidia  of  the  two  fungi,  and  in  view 
of  the  constancy  and  persistence  of  these  points  of  dissimilarity  over  a 
wide  range  of  hosts,  through  several  generations  of  maize  and  during 
three  months’  cultivation,  the  writer  regards  the  Visayan  form  as  worthy 
of  specific  distinction  from  5.  philip pinensis.  The  species,  therefore,  is 
described  as  new,  and  as  it  was  first  found  occurring  spontaneously  on  a 
wild  host,  it  is  named  S.  spontanea. 

DIAGNOSIS 

Sclerospora  spontanea,  n.  sp. 

Symptoms,  effect  on  the  individual  host,  and  destructiveness  to  the  maize  crop 
as  a  whole,  as  previously  described  by  the  writer  for  Sclerospora  philip  pinensis  ( 12 ). 

Mycelial  hyphae  and  haustoria  as  described  for  Sclerospora  philip  pinensis;  but  the 
clavate  hyphae  (conidiophore  initials)  which  emerge  from  the  stomata  are  longer, 
more  slender,  and  more  irregular. 

Conidiophores  as  in  Sclerospora  philip pinensis ,  erect,  single  or  grouped,  develop¬ 
ing  only  at  night  and  in  dew;  comprising  basal  cell,  main  axis,  more  or  less  complex 
dichotomous  branching  system,  and  terminal  sterigmata;  but  differing  in  general 
in  greater  total  length  (350  to  550  n)  and  more  expanded  top,  and  in  particular  as  fol¬ 
lows:  Basal  cell  less  knobbed  and  expanded  at  the  base,  more  slender  (least  diameter 
about  5  to  8  n),  and  longer  (140  to  260  n),  usually  exceeding  or  at  least  equaling  in 
length  the  extent  of  the  main  axis  from  the  septum  to  the  primary  branches.  Main 
axis  usually  expanding  more  abruptly  above  the  septum  to  a  greater  width  (22  to  32  /z) 
and  constricting  noticeably  (to  about  20  n)  below  the  branches.  Branches  longer, 
more  slender,  less  constricted  at  point  of  origin,  less  recurved  and  ascending,  but 
standing  out  more  stiffly.  Sterigmata  longer  (13  /z),  more  slender,  and  straighter. 

Conidia  resembling  those  of  Sclerospora  philip  pinensis  in  hyaline,  finely  granular 
content,  thin  wall,  rounded  apex  lacking  papilla,  and  rounded  base  with  apiculus  of 
attachment,  and  in  invariable  germination  by  tubes;  but  differing  as  follows:  In  shape, 
longer  and  more  slender,  usually  very  elongately  ellipsoid  or  cylindrical;  in  size, 
showing  greater  length  and  less  width,  the  majority  being  39  to  45  n  long  by  15  to  17  n 
in  diameter. 

Oospores  not  yet  encountered  on  maize,  although  an  oogonial  stage  on  Saccharum 
spontaneum  may  prove  to  be  connected. 

Habitat. — Found  in  the  Visayan  group  of  the  Philippine  Islands  principally  on 
cultivated  maize  ( Zea  mays  L.),  rarely  on  the  wild  grass  bugang  ( Saccharum  spon¬ 
taneum  L.),  and  once  on  cultivated  sugar  cane  ( Saccharum  officinarum  L.).  Inocu¬ 
lated  successfully  upon  the  first  two  of  these  hosts  and  also  upon  teosinte  ( Euchlaena 
luxurians  Schrad.),  and  the  wild  grass  Miscanthus  japonicus  (Thunb.)  Anders. 
Extremely  destructive  to  maize,  but  much  less  so  to  the  other  hosts. 


Feh.  i,  1921 


Another  Conidial  Sclerospora  of  Philippine  Maize  679 


Material  of  the  type  will  be  found  in  the  pathologic  collections  of 
the  Bureau  of  Plant  Industry,  Washington,  D.  C.,  and  in  the  herbarium  of 
the  Bureau  of  Science,  Manila,  P.  I. 

7  t 

DISCUSSION 

RELATIONSHIP 

The  two  Sclerosporas,  Sclerospora  spontanea  and  S.  philip pinensis,  are 
undoubtedly  closely  allied  to  each  other.  It  is  even  possible  that  future 
investigation  will  bring  to  light  forms  intermediate  between  them.  Such 
may  be  the  downy  mildew  on  maize  seen  by  Prof.  Reinking  in  the  Cota- 
bato  Valley  and  by  Gov.  Coverston  in  Lanao  Province,  both  of  which 
places  are  in  the  southern  Island  of  Mindanao.  On  the  other  hand, 
the  Mindanao  form  may  be  as  different  from  S.  spontanea  and  5.  philip- 
pinensis  as  these  have  proved  to  be  from  each  other.  The  writer  feels 
confident  that  on  further  search  additional  Sclerosporas  will  be  encoun¬ 
tered  in  the  Philippines  both  on  cultivated  hosts  and  on  wild  grasses. 

The  relationship  of  the  Philippine  downy  mildew  Sclerospora  to  the 
similar  forms  described  on  maize  and  related  crops  from  other  oriental 
countries  has  been  discussed  in  connection  with  Sclerospora  philip  pi¬ 
nensis  ( 12 ).  Unfortunately  the  matter  can  not  be  settled  finally  with 
the  data  available.  As  the  writer’s  discovery  that  suitable  material 
can  be  secured  only  at  night  is  very  recent,  previous  publications  present 
measurements  and  other  data  inadequate  for  comparison  with  living 
material.  In  so  far  as  one  can  judge,  however,  S',  spontanea,  on  account 
of  its  longer,  more  slender  spores,  is  even  more  sharply  distinguished 
than  is  S.  philip  pinensis  from  the  Javan  species,  S.  javanica  Palm  (ro), 
from  the  species  of  British  India,  S.  maydis  (Rac.)  Butl.  (1),  and  from 
the  normal,  short  spored  type  of  the  Formosan  species,  S.  sacchari 
Miyake  (9).  It  is  of  interest  to  note,  however,  that  in  the  greater  length 
of  its  conidia,  the  very  character  wherein  it  differs  so  distinctly  from 
these  other  oriental  species,  S.  spontanea  tends  to  resemble  the  two 
abnormally  long-spored  forms  recorded  by  Japanese  investigators.  In 
his  account  of  S.  graminicola,  Ideta  (8,  p.  1 43-1 45),  in  addition  to  conidia 
of  the  size  characteristic  of  the  species,  mentions  a  class  of  conidia  having 
the — 

shape  of  a  long  ellipse,  38.4  to  57.6  fx  long  by  19.2  to  24  n  wide. 

Also,  Miyake  (9),  in  his  account  of  S.  sacchari,  describes  conidia  not  only 
of  the  usual  shape  and  size,  but  also  of  an  unusual  type — 

long  ovate,  49  to  54  n  by  19  to  23  n. 

The  descriptions  and  drawings  of  both  these  long  types  of  conidia 
remind  one  of  the  spores  of  5.  spontanea,  even  though  the  latter  are 
characteristically  more  slender.  It  is  very  probable  that  the  occur¬ 
rence  of  these  long  conidial  types  in  Japan  and  in  Formosa  indicates  the 


68o 


Journal  of  Agricultural  Research 


VoL  XX,  No.  9 


existence  there  of  strains  or  species  of  Sclerospora  as  yet  unrecognized ; 
but  what  their  relationship  and  significance  may  be,  future  investigation 
must  determine. 

The  relationship  of  these  two  Philippine  conidial  forms  to  the  oogonial 
stage  characteristic  of  the  genus  is  as  yet  unknown.  Whether  Sclero¬ 
spora  pliilippinensis  or  Sclerospora  spontanea  is  connected  with  the  oogonial 
stage  which  is  so  common  on  Saccharum  spontaneum  throughout  the  Philip¬ 
pine  Islands  is  yet  to  be  established.  The  writer  has  attempted  to  germi¬ 
nate  the  oogonia  of  the  latter  and  to  obtain  inoculations  with  them,  but  so 
far  he  has  been  unsuccessful.  Until  the  precise  connection  is  definitely 
established,  it  is  well  to  be  cautious  about  assuming  that  the  two  types 
of  spores  are  with  certainty  different  phases  of  the  same  species.  It 
may  be  worthy  of  note  that  the  writer  has  found,  in  addition  to  the  oogonia 
on  Saccharum  spontaneum,  similar  spores  on  Miscanthus  japonicus  and 
on  cultivated  sugar  cane  in  the  mountains  of  northern  Luzon.  On  all 
these  hosts  the  oogonia  are  apparently  the  same  species;  and  their 
significance  and  importance  will  be  discussed  by  the  writer  in  a  later 
paper. 

NONSPECIALIZATION 

As  the  problem  now  stands,  the  Philippine  maize-mildew  presents  an 
interesting  situation,  since  it  involves  two  causal  Sclerosporas  quite  distinct 
morphologically  but  practically  indistinguishable  physiologically  both  in 
their  effect  on,  and  in  their  virulence  to,  a  range  of  hosts.  The  genus 
Sclerospora  seems,  then,  to  present  a  marked  contrast  to  the  strong 
specialization  of  the  closely  related  genus  Peronospora.  In  the  latter, 
the  work  of  Gaumann  (5,  6,  7)  has  shown  that  the  species  are  strongly 
specialized,  being  distinct  on  different  hosts.  This  is  true  especially  in 
the  Rubiaceae  (7),  but  also  to  a  marked  degree  in  the  Cruciferae  (5)  and 
the  Scrophulariaceae  (6).  The  distinction  holds  both  morphologically, 
in  the  size  and  character  of  the  conidiophores  and  conidia,  and  also 
physiologically,  in  their  inability  to  infect  any  host  species  but  that  from 
which  the  spores  were  derived.  Gaumann,  therefore,  regards  it  as  highly 
improbable  that  the  same  host  species  would  be  found  to  harbor  more 
than  one  species  of  Peronospora.  In  Sclerospora,  however,  we  have 
the  two  species,  Sclerospoi'a  spontanea  and  5.  pliilippinensis,  morpho¬ 
logically  distinct,  yet  both  with  equal  ease  inoculating  the  same  series  of 
hosts,  including  members  not  only  of  the  Maydeae  but  also  of  the  Andro- 
pogoneae. 

SIGNIFICANCE  OF  OCCURRENCE 

The  finding  of  Sclerospora  spontanea  on  a  wild  gramineous  host  is  of 
interest.  Hitherto  in  spite  of  the  attention  which  the  destructive 
oriental  Sclerosporas  have  attracted,  no  conidial  representative  of  the 
genus  has  ever  been  reported  as  occurring  naturally  upon  a  wild  host. 
It  is  a  question  whether  the  occurrence  of  Sclerospora  spontanea  on  wild 


Feb.  i,  1921 


Another  Conidial  Sclerospora  of  Philippine  Maize  681 


Saccharum  in  the  Visayan  Islands  should  be  regarded  as  throwing  light 
on  the  problem  of  the  origin  of  the  Philippine  downy  mildews  of  maize. 
In  the  opinion  of  the  writer  this  and  other  facts  indicate  that  the  native 
grasses  of  the  Philippines  were  the  original  hosts  from  which  the  downy 
mildews  passed  and  are  passing  to  such  very  susceptible  introduced 
crops  as  maize.  On  the  other  hand,  one  should  not  overlook  the  possi¬ 
bility  that  the  wild  Saccharum  clumps  might  have  been  infected  with  the 
downy  mildew  from  badly  diseased  maize  growing  near.  In  this  con¬ 
nection  it  should  be  noted  that  in  two  cases  where  Sclerospora  spontanea 
was  found  on  wild  bugang  grass  ( Saccharum  spontaneum)  the  infected 
clumps  were  so  far  distant  and  so  protected  from  any  downy-mildewed 
maize  that  there  was  little  possibility  of  their  having  been  infected  thus. 
In  the  other  cases  the  infected  bugang  clumps  were  much  older  than  the 
mildewed  maize  adjacent;  and,  because  inoculation  experiments  have 
shown  that  bugang  grass  is  susceptible  only  as  comparatively  young 
seedlings,  there  is  little  doubt  that  the  infection  in  the  grass  clump  had 
been  carried  over  in  the  perennial  rootstocks  and  had  not  been  caught 
from  maize. 

Moreover,  it  is  worthy  of  note,  also,  that  the  wild  Saccharum  is  very 
resistant  to  the  effect  of  the  Sclerospora,  while  maize  is  exceedingly 
unresistant.  In  contrast  to  the  susceptibility  to  severe  injury  already 
noted  in  maize,  wild  Saccharum,  even  though  heavily  infected,  shows 
only  slight  striping  of  the  leaves  (PI.  78,  B,  C),  remains  undeformed,  and 
is  not  materially  retarded  in  development.  In  spite  of  the  downy 
mildew  the  plants  continue  to  grow  vegetatively,  to  produce  flowers 
(PI.  77,  B),  and  to  form,  by  tillering,  dense  clumps  which  by  extensive 
rootstocks  persist  from  season  to  season,  still  supporting  the  active  and 
equally  persistent  parasite.  Because,  as  a  rule,  it  is  the  introduced  host 
which  is  most  injured  by  a  disease  and  the  original,  native  host  which  is 
relatively  unaffected,  the  indications  are  that  wild  Saccharum  and  not 
maize  is  the  original  host  of  Sclerospora  spontanea. 

The  finding  of  Sclerospora  spontanea  on  sugar  cane  is  a  second  point  of 
interest.  Because,  in  Formosa,  the  closely  related  species  5.  sacchari 
Miyake  had  proved  indiscriminately  destructive  to  both  sugar  cane  and 
maize,  the  writer,  while  in  the  Philippines,  made  especial  effort  to  dis¬ 
cover  instances  of  the  transmission  of  downy  mildew  from  one  to  the  other 
of  these  hosts.  The  single  case  in  Cebu,  however,  was  the  only  one  noted. 
In  this  instance  the  single  clump  of  sugar  cane  infected  with  5.  spontanea 
was  situated  at  the  extreme  edge  of  the  field,  separated  only  by  a  narrow 
trail  from  a  large  planting  of  badly  downy-mildewed  maize.  Although 
the  whole  sugar-cane  field  was  carefully  inspected,  no  other  cases  of 
Sclerospora  were  discovered.  It  is  natural  to  infer  that  the  sugar-cane 
plant  was  infected  from  the  neighboring  maize,  especially  since  the  two 
parasites  proved  to  be  the  same.  It  is  rather  surprising,  however,,  that 
this  lone  cane  plant,  of  all  the  thousands  examined  in  scores  of  different 


682 


Journal  of  Agricultural  Research 


Vol.  XX,  No.  9 


fields  adjacent  to  or  even  interplanted  with  infected  maize,  should  be  the 
only  one  to  succumb. 

The  matter  is  still  further  complicated  by  the  fact  that  in  Formosa 
Miyake  easily  obtained  the  infection  of  sugar-cane  plants  grown  from 
cuttings,  while  in  the  Philippines  the  writer  was  not  able  to  inoculate 
cutting-grown  plants  of  sugar  cane,  or  even  of  Saccharum  spontaneum, 
although  seedlings  of  this  grass  were  readily  infected  (PI.  78,  A).  More¬ 
over,  in  Formosa  the  effect  of  Sclerospora  sacchari  Miyake  on  sugar  cane 
is  far  more  destructive  than  was  the  effect  of  Sclerospora  spontanea  on 
this  single  cane  plant.  In  the  former  the  elongation  and  weakening  of 
the  shoots  and  the  conspicuous  yellowish  striping  of  the  leaves  are  a  dis¬ 
tinct  contrast  to  the  stunting  of  the  shoots  and  faint,  pale  green  markings 
of  the  leaves  which  characterized  the  Philippine  specimens.  Also, 
although  the  latter  died  shortly  after  being  transplanted,  this  was  ap¬ 
parently  due  to  the  severe  treatment  they  had  received  rather  than  to 
the  destructive  character  of  the  Sclerospora.  It  is  possible  that  Sclerospora 
spontanea ,  in  its  essential  individuality,  is  much  less  virulent  to  sugar 
cane  than  Sclerospora  sacchari,  or  it  may  be  that  some  limiting  factor  is  oper¬ 
ative  in  the  Philippines.  The  work  of  Fawcett  (4)  indicates  that  tempera¬ 
ture  differences  may  exercise  an  important  limiting  effect  within  a  smaller 
geographic  range  than  from  Cebu  to  Formosa.  In  any  case,  although 
the  matter  is  in  need  of  further  study,  it  can  safely  be  said  that  in  so  far 
as  has  been  observed  in  the  Philippines  the  production  of  sugar  cane  is 
unaffected  by  Sclerospora  spontanea  or  other  conidial  Sclerosporas. 

SUMMARY 

The  downy  mildew  of  maize  which  is  extremely  destructive  in  the 
Philippine  Islands  has  been  found  to  be  caused  by  the  Peronosporaceous 
genus  Sclerospora.  At  first  only  one  species  was  thought  to  be  involved, 
and  this  was  described  by  the  writer  as  Sclerospora  philip pinensis.  More 
recently  the  problem  presented  by  the  Philippine  maize-mildew  has  been 
still  further  complicated,  since  a  second  causal  species  of  Sclerospora  has 
been  found  to  be  concerned  also.  The  foregoing  paper  describes  this 
species  as  new  (S.  spontanea)  and  presents  briefly  its  morphological  and 
physiological  characteristics  and  its  importance  and  relationship. 

Sclerospora  spontanea,  the  more  recently  discovered  form,  occurs  in  the 
Islands  of  Cebu,  Bohol,  and  Leyte,  where  it  was  found  on  the  wild  grass 
Saccharum  spontaneum  L.,  on  sugar  cane  (Saccharum  ofjxcinarum  L.), 
and  on  maize  ( Zea  mays  L.).  Sclerospora  philip  pinensis,  the  species 
first  recognized,  occurs  in  the  Island  of  Luzon,  where  it  was  found  on 
maize,  teosinte  ( Euchlaena  luxurious  Schrad.),  and  sorghum  ( Andropo - 
gon  sorghum  [L.]  Brot.). 

Morphologically,  Sclerospora  spontanea  is  characterized  by  the  rela¬ 
tively  much  greater  length  and  slenderness  of  its  conidiophores  in  general 
and  of  its  basal  eells  and  conidia  in  particular.  In  these  respects  it 
differs  markedly  from  5.  philip pinensis,  which  has  shorter,  stockier 


Feb.  i,  1921 


Another  Conidial  Sclerospora  of  Philippine  Maize  683 


conidiophores,  shorter,  thicker  basal  cells,  and  shorter,  broader  conidia. 
There  are,  moreover,  some  minor  distinctions  between  the  branch  sys¬ 
tems  and  between  the  sterigmata  of  the  two  species. 

These  differences  remain  constant  for  each  species  and  are  not  influ¬ 
enced  by  growth  on  different  hosts  even  through  several  generations. 
Both  species  have  been  artificially  inoculated  with  equal  ease  from  one 
to  another  of  the  following  hosts:  Maize,  teosinte,  Miscanthus  japonicus, 
and  Saccharum  spontaneum.  Attempts  to  inoculate  sorghum  artificially 
were  unsuccessful  with  both  species.  Because  no  seedlings  of  sugar 
cane  were  available,  no  inoculation  with  either  fungus  was  attempted. 
Inoculations  on  sprouted  sugar-cane  cuttings  were  uniformly  unsuccessful. 

Since  the  size  and  shape  of  the  conidia  are  the  most  useful  criteria  of 
interspecies  distinction,  they  are  given  in  detail.  Measurements  of  700 
conidia  of  each  of  the  two  species  were  combined  into  comparative  tables 
and  graphs  of  frequency  distribution  in  an  attempt  to  present  the  dif¬ 
ferences  between  them  quantitatively  as  well  as  qualitatively. 

Although  morphologically  the  two  species  differ  as  has  been  described, 
yet  physiologically,  in  general  effect  in  the  field,  in  effect  on  the  individual 
plant,  and  in  virulence  to  the  same  wide  range  of  hosts  no  distinction 
between  them  is  apparent. 

The  discovery  that  two  forms  are  involved  complicates  the  problem 
presented  by  the  Philippine  downy  mildew  of  maize.  Because  two 
forms  morphologically  different  but  practically  indistinguishable  in 
physiologic  effect  are  concerned  in  the  same  disease,  there  appears  to 
be  a  decided  lack  of  that  specialization  which  characterizes  certain  other 
genera  of  the  Peronosporaceae.  It  seems  highly  probable  that  still 
other  forms  will  be  found  to  be  concerned  in  similar  diseases  in  the 
Philippine  Islands  and  throughout  the  Orient. 

In  addition  to  these  two  conidial  species  with  a  host  range  of  maize, 
teosinte,  sorghum,  sugar  cane,  Saccharum  spontaneum ,  and  Miscanthus 
japonicus,  the  writer  has  encountered  in  the  Philippines  oogonial  stages 
of  Sclerospora  on  Saccharum  spontaneum,  Saccharum  officinarum,  and 
M.  japonicus.  The  oogonia  on  these  three  hosts  are  practically  indis¬ 
tinguishable.  Whether  these  oogonial  and  conidial  stages  are  quite 
unrelated  or  are  indeed  only  phases  in  the  development  of  the  same 
organism  remains  to  be  determined. 

Sclerospora  spontanea,  like  S.  philip pinensis ,  is  closely  related  to  the 
other  conspicuous  conidial  Sclerosporas  of  the  Orient:  5.  javanica  Palm, 
of  Java;  5.  maydis  (Rac.)  But.,  of  India;  and  5.  sacchari  T.  Miyake,  of 
Formosa.  All  these  forms  are  characterized  by  the  predominance  of 
the  conidial  stage,  the  absence  or  great  rarity  of  the  oogonia,  germina¬ 
tion  of  the  conidia  by  tubes,  and  the  occurrence  on  maize,  sugar  cane, 
and  related  hosts  in  the  Orient.  5.  spontanea,  however,  because  of  its 
longer,  more  slender  spores  is  as  a  species  distinguished  even  more 
sharply  than  5.  philip  pinensis  from  these  other  oriental  representatives. 


684 


Journal  of  Agricultural  Research 


Vol.  XX,  No.  9 


The  discovery  of  Sclerospora  spontanea  on  wild  Saccharum  spontaneum 
is,  in  so  far  as  the  writer  is  aware,  the  first  record  of  the  occurrence  of  a 
conidial  Sclerospora  on  a  wild  host  in  the  Orient.  This  occurrence,  in 
connection  with  other  data,  seems  to  the  writer  to  indicate  that  the  wild 
grasses  are  the  natural  hosts  of  these  oriental  downy  mildews  from  which 
they  have  passed  and  are  passing  to  susceptible  introduced  crops  such 
as  maize. 

LITERATURE  CITED 

(1)  Butler,  E.  J. 

1913.  THE  DOWNY  MILDEW  OF  MAIZE  (SCLEROSPORA  MAYDIS  (RAC.)  BUTL.). 

In  Mem.  Dept.  Agr.  India  Bot.  Ser.,  v.  5,  no.  5,  p.  275-280,  pi.  8-9 
(1  col.). 

(2)  Davenport,  C.  B. 

1904.  STATISTICAL  METHODS,  WITH  SPECIAL  REFERENCE  TO  BIOLOGICAL  VARIA¬ 
TION.  Ed.  2,  rev.  223  p.,  diagrs.  New  York.  Bibliography,  p.  84-104. 

(3)  Davenport,  Eugene. 

[01907].  principles  of  breeding.  727  p.,  illus.  Boston,  New  York. 

(4)  Fawcett,  Howard  S. 

1917.  PRELIMINARY  NOTE  ON  THE  RELATION  OF  TEMPERATURE  TO  THE  GROWTH 

OF  certain  parasitic  fungi  in  cultures.  In  Johns  Hopkins  Univ. 
Circ.  203  (n.  s.,  3),  p.  193-194. 

(5)  Gaum ann,  Ernst. 

1918.  UBER  DIE  FORMEN  DER  PERONOSPORA  PARASITICA  (PERS.)  FRIES.  In 

Beih.  Bot.  Centralbl.,  Bd.  35,  Abt.  1,  Heft  3,  p.  395-533,  47  fig.  Zitierte 
Literatur,  p.  531-533. 

(6)  - 

1918.  UBER  DIE  SPEZIALISATION  DER  PERONOSPORA  AUF  EINIGEN  SCROPHULARIA- 
CEEN.  In  Ann.  Mycol.,  v.  16,  no.  1/2,  p.  189-199,  6  fig.  Zitierte  Litera¬ 
tur,  p.  199. 

(7)  - 

1918.  UBER  DIE  SPEZIALISATION  DER  PERONOSPORA  CALOTHECA  DE  BARY. 

In  Svensk  Bot.  Tidskr.,  Bd.  12,  Hafte  4,  p.  433-445,  2  fig.  Literatur- 
verzeichnis,  p.  445. 

(8)  Ideta,  Arata. 

1914.  HANDBUCH  DER  PFLANZENKRANKHEITEN  JAPANS.  Ed.  4  enl.,  936  p., 

illus.,  24  pi.  (8  col.).  Tokyo.  1909-11.  Text  in  Japanese;  indexes 
and  bibliography  (7  p.)  in  German,  etc.  Added  title-pages  in  Japa¬ 
nese,  English,  and  French.  A  second  Japanese  t.-p.,  states  that 
this  is  ed.  6,  1914. 

(9)  Miyake,  Tsutome. 

1911.  ON  A  FUNGUS  DISEASE  OF  SUGARCANE  CAUSED  BY  NEW  PARASITIC 

fungus,  sclerospora  sacchari  t.  miy.  In  Rpt.  Sugar  Exp.  Sta- 
Govt.  Formosa,  Div.  Path.  Bui.  1,  61  p.,  9  pi.  In  Japanese. 

(10)  Palm,  Bj. 

1918.  ONDERZOEKINGEN  OVER  DE  OMO  LIJER  VAN  DE  MAIS.  (With  an  English 
summary.)  In  Meded.  Lab.  Plantenziekten  [Batavia],  no.  32,  78  p., 
8  pi. 

(11)  Rosenbaum,  J. 

1917.  studies  of  the  genus  phytophthora.  In  Jour.  Agr.  Research,  v.  8. 
no.  7,  p.  233-276,  13  fig.,  pi.  71-77.  Literature  cited,  p.  273-276. 

(12)  Weston,  William  H.,  Jr. 

1920.  Philippine  downy  mildew  of  maize.  In  Jour.  Agr.  Research,  v.  19, 
no.  3,  p.  97-122,  3  fig.,  pi.  A-B  (col.),  16-25.  Literature  cited,  p.  121- 
122. 


PLATE  76 1 

Comer  of  a  native-grown  maize  plot  in  the  interior  uplands  of  Cebu.  At  the  edge 
of  this  field,  in  which  many  maize  plants  were  being  killed  by  downy  mildew,  were 
occasional  clumps  of  the  wild  grass  ( Saccharum  spontaneum  L.)  called  “bugang"  in 
the  Visayan  Islands.  One  of  these  clumps,  which  was  severely  infected  with  Sclero- 
spora  spontanea,  is  shown  at  the  left.  The  older,  primary  stalk  of  this  clump,  had  died, 
but  although  the  remaining  shoots  were  apparently  uninjured,  great  numbers  of 
conidiophores  were  being  produced  on  them,  especially  on  the  one  held  out  for  inspec¬ 
tion.  The  base  of  this  shoot  was  a  few  feet  farther  down  the  steep  slope  at  the  point 
indicated  by  the  arrow.  Behind  the  central  figure  can  be  seen  a  maize  plant  notice¬ 
ably  discolored  by  the  downy  mildew. 


1  Photographs  by  W.  H.  Weston. 


Another  Conidial  Sclerospora  of  Philippine  Maize 


Plate  76 


Journal  of  Agricultural  Research 


Vol.  XX,  No.  9 


Another  Conidial  Sclerospora  of  Philippine  Maize 


Plate  77 


Journal  of  Agricultural  Research 


Vol.  XX.  No.  9 


PLATE  77 

A.  — Clump  of  Saccharum  spontaneum,  showing  characteristic  size  and  habit  of 
healthy  plants  under  natural  conditions.  The  measure  is  2  meters  tall. 

B.  — Clump  of  Saccharum  spontaneum  infected  with  Sclerospora  spontanea.  When 
transplanted  to  this  container  in  Cebu  the  infected  plant  comprised  a  single  shoot 
separated  from  the  clump  shown  in  the  preceding  plate.  This  shoot  continued  to 
develop  vigorously  in  spite  of  the  downy  mildew  until  after  5X  months  it  had  produced 
the  thriving  clump  shown.  Conidiophores  were  still  being  produced  in  abundance, 
especially  by  the  younger  stalks.  Same  measure  as  in  A. 


PLATE  78 


A.  — A  young  seedling  (3  weeks  old)  of  Saccharum  spontaneum  infected  with 
Sclerospora  spontanea.  On  this  seedling,  which  was  artificially  inoculated  on  the 
second  night  after  it  emerged,  conidium  production  began  on  the  sixth  night  following 
and  recurred  in  increasing  abundance  on  successive  nights.  In  contrast  to  healthy 
seedlings  this  plant  betrays  the  effect  of  the  Sclerospora  in  its  pallor  and  in  the  presence 
of  a  whitish  “down”  of  conidiophores.  These  have  collapsed  on  drying  but  can  still 
be  seen  on  that  part  of  the  fourth  leaf  indicated  by  the  pointer.  X  A- 

B.  — Conidiophores  on  the  leaf  of  Saccharum  spontaneum.  A  portion  of  the  upper 
leaf  surface  of  a  downy-mildewed  plant  (PI.  77,  B)  showing  remains  of  the  whitish 
“down”  of  innumerable  conidiophores  produced  diming  the  night.  Although  photo¬ 
graphed  as  early  as  light  would  permit,  the  leaf  surface  has  dried  somewhat  and  the 
fragile  conidiophores  have  shrunk  and  matted  together.  X  i>£. 

C.  — Young  shoots  of  Saccharum  spontaneum  arising  after  the  primary  stalk  had  been 
cut,  and  like  it  severely  infected  with  Sclerospora  spontanea.  The  main  plant,  one  of 
the  four  downy-mildewed  ones  transplanted  from  Cebu,  was  cut  off  close  to  the  ground. 
All  the  subsequent  shoots  arising  from  the  remaining  base  were,  from  the  first  leaf, 
badly  infected  with  Sclerospora  and  produced  abundant  conidiophores. 


Another  Conidial  Sclerospora  of  Philippine  Maize 


Plate  78 


Journal  of  Agricultural  Research 


Vol.  XX,  No.  9 


Another  Conidial  Sclerospora  of  Philippine  Maize 


Plate  79 


4 


Journal  of  Agricultural  Research 


Vol.  XX,  No.  9 


PLATE  79  1 


A.  — Typical  conidiophore,2  showing  characteristically  long,  slender,  unknobbed 
basal  cell,  relatively  short  main  axis  with  its  greatest  diameter  about  midway  to  the 
primary  branches,  and  fairly  well-developed  branch  system  bearing  long,  slender 
conidia.  The  number  of  conidia  is  somewhat  less  than  that  usually  encountered. 
From  maize  inoculated  from  Saccharum  spontaneum.  X  375. 

B.  — Upper  portion  of  a  conidiophore  which  has  a  poorly  developed  branch  system 
and  hence  bears  few  conidia  on  sterigmata  which  are  relatively  large.  Several  conidia 
have  been  broken  off  in  mounting.  From  maize.  X  375. 

C.  — Portion  of  the  branch  system  of  a  conidiophore,  showing  the  conidia  germinat¬ 
ing  while  still  attached  to  their  sterigmata.  From  maize.  X  375. 

D.  — Stalk  portion  of  a  typical  conidiophore,  showing  long,  slender,  unknobbed 
basal  cell,  and  main  axis  which  is  slender  above  the  septum,  expands  rapidly  to  its 
greatest  diameter  about  midway,  and  contracts  again  below  the  branches.  From 
Saccharum  spontaneum.  X  375- 

E.  F. — Typical  basal  cells  of  conidiophores.  E  from  Saccharum  spontaneum;  F 
from  sugar  cane.  X  375- 

G.  — Stalk  portion  of  a  conidiophore  with  basal  cell  which,  though  unusually  short, 
nevertheless  is  longer  than  the  extent  of  the  main  axis  from  septum  to  primary 
branches.  From  Saccharum  spontaneum.  X  375. 

H.  — Typical  stalk  portion  of  a  conidiophore  from  sugar  cane.  Compare  with  A 
and  D.  X  375- 

I.  J,  K. — Typical  conidia  showing  variations  in  size  and  shape  and  method  of  ger¬ 
mination  by  hyphae.  I  from  maize,  the  lowest  figure  from  material  especially  fixed 
and  stained  to  bring  out  the  internal  structure;  J  from  Saccharum  spontaneum;  K 
from  sugar  cane.  X  375. 


1  The  drawings  were  made  with  the  aid  of  a  camera  lucida.  Figure  A  aud  the  ungerminated  conidia  of 
figures  I,  J,  and  K  are  from  fresh  material.  All  the  other  drawings  are  from  preserved  specimens. 

2 In  comparing  these  drawings  with  the  plates  of  Sclerospora  philip pinensis  ( 12 )  it  should  be  noted  that 
the  latter  give  a  somewhat  misleading  impression  of  the  relative  spreading  of  the  branch  system  because 
the  conidiophores  were  flattened  slightly  in  mounting. 


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